1. Field of the Invention
The invention generally relates to the satellite positioning system based guidance of munitions, and in particular, to guidance for an artillery round such that the artillery round is a precision weapon.
2. Description of the Related Art
The military use of artillery is well known. One drawback of conventional artillery, such as rockets, mortar rounds, artillery shells, and the like, is that without a guidance system, such artillery rounds can have a relatively large Circular Error Probable. The Circular Error Probable can grow large especially when distance is great and/or wind conditions are unstable. Without guidance, a relatively large number of munitions may be needed to ensure the destruction of a target. This can be costly both in terms of munitions and in physical resources that, with precision guidance, could otherwise be allocated to additional targets. In addition, the amount of collateral damage can be higher than desired.
When precision guidance is employed, the Circular Error Probable can be dramatically reduced. This permits a cost savings in the number of rounds, reduces the warning from earlier-fired rounds, reduces collateral damage, increases the effectiveness of a combat unit, and can even decrease the amount of training needed or data used (such as wind condition data).
One precision GPS-guided munition is the M982 Excalibur, which is a 155 mm guided artillery shell. While effective, the M982 Excalibur is expensive.
The XM1156 Precision Guidance Kit is a kit that replaces the existing fuze of a standard projectile. Accordingly, the costs are expected to be much less.
One system for guiding a projectile is taught in U.S. Pat. No. 6,981,672 to Clancy, et al. (“Clancy”). With reference to FIG. 1 of Clancy, canards 12 and 14, are spin canards, which enable the nose assembly 10 to counter rotate with respect to the rest of the projectile. Canards 16 and 18 steer the round. When the nose assembly 10 is spinning, the steering from the canards 16 and 18 has no net effect on flight trajectory. When the nose assembly 10 is despun, the canards 16 and 18 provide steering based on the rotational orientation of the canards 16 and 18 in the despun state. Despinning is accomplished via a brake. The brake imparts a torque to the nose assembly 10 in the direction of the spinning projectile. By balancing the torque from the spin canards and the brake, the rotational orientation of the nose assembly 10 can be adjusted.
Another system for guiding a projectile is taught in U.S. Pat. No. 7,354,017 to Morris, et al. (“Morris”). With reference to FIG. 1 of Morris, counter rotation fins 42 spin the guidance package 41. When the guidance package 41 is despun, the control surfaces 15 steer the projectile according to the rotational orientation of the control surfaces 15 in the despun state.